The present invention relates to a surround array speaker apparatus which is high in the degree of freedom of selection of an installation place.
In recent years, array speaker apparatus capable of producing a surround sound field though they employ a single body (refer to Patent document 1, for example). The array speaker apparatus disclosed in Patent document 1 is a system capable of expressing a sound field expanse in the right-left and front-rear directions by means of only a single speaker that is disposed in front of a listener and hence is called a front surround system. Employing a single body as mentioned above, this array speaker apparatus does not require installation of plural speakers and related wiring and can thus be installed easily.
FIG. 1 shows the principle of an array speaker and a surround sound field as generated by an array speaker apparatus. The array speaker apparatus disclosed in Patent document 1 operates according to the principle of the delayed array. As shown in FIG. 1A, the same acoustic signal is input, with delays that are a little different from each other, to plural speaker units SPa-SPe that are arranged in line or in a plane so as to produce a sound field as would be produced when speaker units SPa′-SPe′ emit sounds simultaneously. Resulting sounds simultaneously reach a single point F (focal point) in the space and the acoustic energy around the focal point F is intensified through in-phase addition. In this manner, sound beams having high directivity toward the focal point F can be generated. This technique is called the delayed array. In array speaker apparatus, audio signals for generating multichannel sound beams can be input to each speaker unit in superimposition because the system including the speaker units constituting the array speaker and the space to which sounds are emitted from the speaker units are generally a linear system. As shown in FIG. 1B, an array speaker apparatus 1 produces, around a listener H, a surround sound field corresponding to a moving picture being displayed on a monitor 3 by generating virtual sound sources by emitting plural (i.e., multichannel) sound beams simultaneously and causing them to be reflected by walls.    [Patent document 1] JP-A-2006-238155
To produce a surround sound field or generate localized virtual sound sources in directions that are different from the direction of the speaker by an array speaker, the following two conditions should necessarily be satisfied:
1) To produce a surround sound field or generate virtual sound sources in directions that are different from the direction of the speaker, the presence of walls that reflect sound beams and thereby localize virtual sound sources is indispensable.
2) To localize virtual sound sources on walls, sound beams that reach a listener after being reflected by the walls should be sufficiently stronger than a sound that reaches the listener directly from the speaker (inverse to the precedence effect). Furthermore, since the sound attenuates according to the ratio between distances, virtual sound sources cannot be localized if the lengths of sound beam paths are much different from the length of a direct sound path. Therefore, the ratios between the lengths of the reflection sound beam paths and the length of the direct sound path should be set in a certain range. Still further, in a near sound field, the interference between speaker units is remarkable and one can notice a variation between their frequency characteristics. Therefore, the listening position needs to be spaced from the speaker units to some extent. That is, it is indispensable to set a certain distance between the speaker and the listener.
However, a listener's room is not necessarily ideal: a speaker may be installed in such a manner as not to be suitable for generation of surround sounds by an array speaker (e.g., the distances between the listener and the left and right walls are much different from each other or the speaker is set obliquely at a corner of the room). If the speaker is installed in such a state (particularly in the case where wall reflection is used for the front-left and front-right channels), the audibility is lowered because of insufficient reflection or right/left-unbalanced reflection. There is another problem that if a direct sound is used, a sufficient sense of separation cannot be obtained because of the employment of the single body.